I am in the process of building my first system and have read that a hydroton filled growbed must be 300mm deep. my question is weather a gravel filled growbed can be made more shallow?, I've seen one at 100mm on utube. I will be building inside a polytunnel and i think gravel may help me in a cold climate, it's warm today at 16 degrees c.
Hi Kevin, I am not convinced Hygroton is worth the extra expense. I bought 75 lbs and it was over $50 to ship it to me!! To fill my 10 inch bed, I used pea gravel, lava rock and Hygroton. First two, even at Lowe's Hardware in 10 lb bags was 1/10 the cost per pound of the other. I recommend use material that is local/cheap that will not adversely affect your pH. Greg
Hi Kevin. I'll start this of with my 2-cents. I'm a big believer in 11 - 12" (300 mm) of grow bed depth no matter if you are using gravel or hydroton. While you can get away with a shallower bed, and many do, what a 300 mm bed gives you is at least 3 benefits. 1) Flexibility with what you plant. You just don't have to think about what you are planting and what kind of space in the root zone it needs if you go with 300mm, from carrots to massive cucumber plants. You will never worry about them toppling over 2) it will give you plenty of temperature insulation at the root zone and help moderate temperature fluctuations, 3) there seems to be some good juju that happens with the biology of the bacteria when it is able to stratify into multiple layers. This is out of my expertise, but I have heard it from the experts and I believe it. Perhaps a 4th would be that some of the most successful media based aquaponic growers (Joel Malcom, Murray Hallam, Travis Hughey) all advocate a 300mm depth.
OK, enough of my blathering...what does everyone else think?
If you are in a McMurtry flood and drain system then what he reccomends is 300mm at the input end and ~330 cm at the further end where it will drain out at the bottom. Thats approx. 12" at the input and 15-16" at the drain end.
What are you planning on growing?
The 300 mm depth is with sand or other media. Sand or gravel is most economical.